The rapid and effective repair of bone defects caused by injury, disease, wounds, or surgery is a goal of orthopedic surgery. Toward this end, a number of compositions and materials have been used or proposed for use in the repair of bone defects. The biological, physical, and mechanical properties of the compositions and materials are among the major factors influencing their suitability and performance in various orthopedic applications.
Autologous cancellous bone (“ACB”), also known as autograft or autogenous bone, is considered the gold standard for bone grafts. ACB is osteoinductive and nonimmunogenic, and, by definition, has all of the appropriate structural and functional characteristics appropriate for the particular recipient. Unfortunately, ACB is only available in a limited number of circumstances. Some individuals lack ACB of appropriate dimensions and quality for transplantation, and donor site pain and morbidity can pose serious problems for patients and their physicians.
Much effort has been invested in the identification or development of alternative bone graft materials. In the procurement and processing of xenograft or allograft, a prime consideration is minimizing the risk of transferring potentially harmful diseases to the bone recipient. In fact, provision of bulk bone tissue safe for transplantation provides a very special challenge as immunogenic material and also microorganisms and viruses can be found deep within the internal matrix of bone samples.
Transplanting contaminated bone can have serious consequences to the recipient. For example, transmission of human immunodeficiency virus (HIV) via bone grafting is well known. Accordingly, there is a great need for bone processing methods that decrease the risk of disease transmission associated with the use of, preparation and procurement of, transplantable bone to the recipient. In this regard it is also important to recognize that even if state of the art donor screening methodology is used, recent infections in a particular donor may not be detected, thereby underscoring the importance of improved cleaning and decontaminating treatments that offer prophylactic protection against potential, or as yet undetected, infectious agents.
In addition, of increasing concern is the presence of infectious prions in biologically derived materials used for xeonografts and prosthetic devices. The widespread occurrence of prion-related disease and the possibility of interspecies transmission has serious implications for the biotechnology industry, which derives many of its products from mammalian tissue, including bone. Prions are more resistant toward inactivation than more conventional pathogens such as viruses or bacteria. Thus, relatively harsh conditions are required to decontaminate prion-containing biological materials. The only methods currently known to disinfect prion contaminated biological preparations are prolonged autoclaving at 130° C. or above, and treatment with concentrated sodium hydroxide solution.
Another concern is the presence of pyrogens. Pyrogens are substances which, even in an extremely small amount, cause abnormal elevations in the body temperatures of a patient and in extreme cases can cause fatal shock. A pyrogen can be endogenous or exogenous to the body. If a pyrogen finds its way into the bloodstream of a patient such as, for example, by intravenous injection of a medicine, it can cause a violent exothermic reaction independently of the principal action of the medicine. In some embodiments, a pyrogen can consist of any class of biological macromolecule including proteins, nucleic acids, carbohydrates, or lipids. There are a few methods to remove pyrogens from solutions. However, pyrogen removal can be difficult due to the high variability of their molecular weight and because they are relatively thermally stable and insensitive to pH changes.
One method of treating contaminated bone is sterilization. A variety of physical or chemical methods have been developed for use in sterilization and include, for example, exposure to chemicals or heat, or exposure to ionizing or non-ionizing radiation. Exemplary sterilization methods include treating prosthesis and graft components with chemical reagents. However, the chemical reagents themselves, or reaction byproducts derived from the reagents, can be harmful to the intended recipient of the prosthetic device. Accordingly, such chemicals must be removed prior to implantation of the devices. Common chemical sterilizing agents include ethylene oxide and formaldehyde, both of which are alkylating agents and, therefore, can modify and inactivate biologically active molecules. For example, ethylene oxide modifies the bone structure and negatively affects osteoinductivity. Both of these chemicals are, however, known to be carcinogens and mutagens.
Current methods for viral inactivation and sterilization involve the use of toxic chemicals, high temperature and/or irradiation. The harsh treatment of biological active materials such as bone grafting materials cause the degradation or decomposition of materials, destroy biological activity, for example osteoconductivity of demineralized bone matrix, and reduce mechanical properties significantly.
There are also significant limitations on the extent to which decontaminating agents have been used successfully to penetrate and to decontaminate matrix of bone. Bone matrix contains potentially removable materials, for example, marrow, cells and lipids that impede access of decontaminating agents deep into bulk bone tissue where infectious agents or immunogenic macromolecules may be present.
Accordingly, there is a need for methods of removing/destroying unwanted substances from bulk tissue material (e.g., frozen bulk bone tissue) including, but not limited to water, viruses, pyrogens, micro-organisms, pathogens and lipids so as to dry, clean, sterilize, delipidate and/or to depyrogenate, and to aid in the storage and/or further processing of the tissue.